Historically our concepts of recombination have been derived from genetical studies of higher organisms. Unfortunately little biochemical information from eucaryotes about enzymes and proteins involved in recombination is known. The proposed research has as its goal the elucidation of the mechanism of genetic recombination through biochemical characterization of enzymes and proteins involved in the macromolecular DNA metabolism of a simple eucaryote. The organism selected for study is Ustilago maydis, a yeast-like fungus whose genetic system is well characterized. Enzymes likely to be involved in recombination such as deoxyribonucleases, ATPases, topoisomerases, and reannealing enzymes will be purified and characterized. Mutants known to be defective in various steps in recombination such as gene conversion and crossing over and in the overlapping areas of DNA repair and replication are available to help establish the biological role of enzymes of interest. Studies on several previously identified enzymes from Ustilago will be continued. The methods that will be used in this study include physical methods (ultracentrifugation, gel electrophoresis, electron microscopy) and biochemical methods (column chromatography of enzymes, radio labeling and purification of nucleic acids).